Semiconductor device capable of high-voltage operation

ABSTRACT

A semiconductor device includes a semiconductor substrate having a first conductivity type, a first well region formed in a portion of the semiconductor substrate, having a second conductivity type that is the opposite of the first conductivity type. A second well region is formed in a portion of the first well region, having the first conductivity type. A first gate structure is formed over a portion of the second well region and a portion of the first well region. A first doped region is formed in a portion of the second well region. A second doped region is formed in a portion of the first well region, having the second conductivity type. A second dielectric layer is formed over a portion of the first gate structure, a portion of the first well region, and a portion of the second doped region.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of pending U.S. Ser. No. 16/225,077,filed on Dec. 19, 2018, which is a Continuation of Ser. No. 15/411,099,filed on Jan. 20, 2017 (now U.S. Pat. No. 10,199,496, issued on Feb. 5,2019), which claims the benefit of U.S. Provisional Application No.62/306,661 filed Mar. 11, 2016, the entirety of which is incorporated byreference herein.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to integrated circuits (ICs), and inparticular to semiconductor devices capable of high-voltage operationand methods for forming the same.

Description of the Related Art

Recently, as demand has increased for high-voltage devices such as powersemiconductor devices, there has been an increasing interest in researchon high-voltage metal-oxide-semiconductor field effect transistors (HVMOSFETs) applied in high-voltage devices.

Among the various types of high-voltage metal-oxide-semiconductor fieldeffect transistors (HV MOSFETs), semiconductor devices such as lateraldouble diffused metal-oxide-semiconductor (LDMOS) devices are oftenused.

However, with progress being made in semiconductor fabrication, thebreakdown voltage of high-voltage MOSFETs for high-voltage devices needsto be increased further. Thus, a reliable high-voltage MOSFET forhigh-voltage devices having an increased breakdown voltage is needed tomeet device performance requirements as the needs in semiconductorfabrication of high-voltage devices continue.

BRIEF SUMMARY OF THE INVENTION

An exemplary semiconductor device comprises a semiconductor substrate, afirst well region, a second well region, a first gate structure, a firstdoped region, a second doped region, and a second gate structure. Thesemiconductor substrate has a first conductivity type, and the firstwell region formed is in a portion of the semiconductor substrate,having a second conductivity type that is the opposite of the firstconductivity type. The second well region is formed in a portion of thefirst well region, having the first conductivity type. The first gatestructure is formed over a portion of the second well region and aportion of the first well region. The first doped region is formed in aportion of the second well region, having the second conductivity type.The second doped region is formed in a portion of the first well region,having the second conductivity type. The second gate structure is formedover a portion of the first gate structure, a portion of the first wellregion, and a portion of the second doped region.

An exemplary method for forming a semiconductor device comprisesproviding a semiconductor structure comprising a first gate structure, afirst well region, and a second doped region, and forming a second gatestructure over a portion of the first gate structure, a portion of thefirst well region, and a portion of the second doped region. Thesemiconductor structure further comprises a semiconductor substrate, asecond well region, a first gate structure, and a first doped region.The semiconductor substrate has a first conductivity type, and the firstwell region is formed in a portion of the semiconductor substrate,having a second conductivity type that is the opposite of the firstconductivity type. The second well region is formed in a portion of thefirst well region, having the first conductivity type. The first dopedregion is formed in a portion of the second well region, having thesecond conductivity type. The second doped region is formed in a portionof the first well region, having the second conductivity type. The firstgate structure is formed over a portion of the second well region and aportion of the first well region.

Another exemplary method for forming a semiconductor device comprisesproviding a semiconductor structure comprising a first gate structure, afirst well region, and a second doped region in a first region, and anisolation element in a second region, and simultaneously forming asecond gate structure over a portion of the first gate structure, aportion of the first well region, and a portion of the second dopedregion in the first region, and a third gate structure over a portion ofthe isolation element in the second region. The semiconductor structurefurther comprises a semiconductor substrate, a second well region, afirst gate structure, and a first doped region. The semiconductorsubstrate has a first conductivity type, and the first well region isformed in a portion of the semiconductor substrate in the first region,having a second conductivity type that is the opposite of the firstconductivity type. The second well region is formed in a portion of thefirst well region, having the first conductivity type. The first dopedregion is formed in a portion of the second well region, having thesecond conductivity type. The second doped region is formed in a portionof the first well region, having the second conductivity type. The firstgate structure is formed over a portion of the second well region and aportion of the first well region. The isolation element is formed in aportion of the semiconductor substrate in a second region that isdifferent from the first region. The third conductive layer is formedover the isolation element.

A detailed description is given in the following embodiments withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention can be more fully understood by reading the subsequentdetailed description and examples with references made to theaccompanying drawings, wherein:

FIG. 1 is schematic cross section showing an intermediate stage of amethod for forming a semiconductor device according to an embodiment ofthe invention;

FIG. 2 is schematic cross section showing an intermediate stage of amethod for forming a semiconductor device according to an embodiment ofthe invention;

FIG. 3 is schematic cross section showing an intermediate stage of amethod for forming a semiconductor device according to an embodiment ofthe invention;

FIG. 4 is schematic cross section showing an intermediate stage of amethod for forming a semiconductor device according to an embodiment ofthe invention;

FIG. 5 is schematic cross section showing an intermediate stage of amethod for forming a semiconductor device according to an embodiment ofthe invention; and

FIG. 6 is schematic cross section showing an intermediate stage of amethod for forming a semiconductor device according to an embodiment ofthe invention.

DETAILED DESCRIPTION OF THE INVENTION

The following description is of the best-contemplated mode of carryingout the invention. This description is made for the purpose ofillustrating the general principles of the invention and should not betaken in a limiting sense. The scope of the invention is best determinedby reference to the appended claims.

FIGS. 1-6 are schematic cross sections showing a method for forming asemiconductor device according to an embodiment of the invention,respectively showing an intermediate stage of the method. Thesemiconductor device formed by the method shown in FIGS. 1-6 comprises ahigh-voltage metal-oxide-semiconductor field effect transistor (HVMOSFET) capable of high-voltage (e.g. 100 volts or above) operations.

In FIG. 1, a substantially fabricated semiconductor structure isprovided. As shown in FIG. 1, the semiconductor structure is providedwith two different regions A and B. Region B can be adjacent to region Aor separated from region A by another region (not shown) formedtherebetween.

As shown in FIG. 1, the semiconductor structure in region A comprises asemiconductor substrate 100 such as a silicon substrate. Thesemiconductor substrate 100 may have a first conductivity type such asP-type. An isolation element 108 is respectively disposed in oppositeend portions of the substrate 100 in region A. The isolation elements108 can be the shallow trench isolation (STI) elements shown in FIG. 1,but are not limited thereto. In some embodiments, the isolation elements108 can be field oxide (FOX) isolation elements. The isolation elements108 may comprise insulating materials such as silicon oxides, but theyare not limited thereto. A deep well region 102 is formed in a portionof the semiconductor substrate 100 underlying the isolation elements108. The deep well region 102 may have a second conductive type that isthe opposite of the first conductivity type, for example N-type.Moreover, a well region 104 is formed between the deep well region 102and each of the isolation elements 108. A well region 106 is formed in aportion of the semiconductor substrate between the well regions 104, andis above the deep well region 102. The well regions 104 and the wellregion 106 may have the first conductivity type, for example P-type. Awell region 110 is formed in the semiconductor substrate 100 between theisolation elements 108, the well region 106 and the well regions 104.The well region 110 may have the second conductive type, for exampleN-type. A well region 112 is formed in a portion of the well region 110and is adjacent to the one isolation element 108. The well region 112may have the first conductivity type, for example P type. A doped region114 is formed in a portion of the well region 112, and may have thesecond conductivity type, for example N-type. Another doped region 116is formed in a portion of the well region 110, and is adjacent to theright isolation element 108. The doped region 116 may have the secondconductivity type, for example N-type. The doped regions 114 and 116 mayhave a doping concentration greater than that of the well region 110.

In region A, a gate structure G1 is formed over a portion of the wellregion 112 and a portion of the well region 110, comprising a dielectriclayer 118 and a conductive layer 120 formed over the dielectric layer118. In one embodiment, in region A, the gate dielectric layer 118 maycomprise silicon oxide, silicon nitride or the like, and may have athickness of about 23-140 Å. The conductive layer 120 may compriseconductive materials such as polysilicon, metal or the like, and mayhave a thickness of about 800-2000 Å.

In addition, the semiconductor structure in region B further comprisesanother isolation element 108 formed in a portion of the substrate 100.Another gate structure G2 is formed over a portion of the isolationelement 108, comprising the dielectric layer 118 and the conductivelayer 120. In one embodiment, in region B, the gate dielectric layer 118may comprise silicon oxide, silicon nitride or the like, and may have athickness of about 23-140 Å. The conductive layer 120 may compriseconductive materials such as polysilicon, metal or the like, and mayhave a thickness of about 800-2000 Å.

In FIG. 2, a dielectric layer 122 is conformably formed over thesemiconductor structure shown in both regions A and B shown in FIG. 1,covering the top surface of the semiconductor substrate 100 and exposedsurfaces of the gate structures formed one the semiconductor substrate100. In one embodiment, the dielectric layer 122 may comprise siliconoxide, silicon nitride or the like, and may have a thickness of about200-1200 Å. The dielectric layer 122 may be thicker than the dielectriclayer 118.

In FIG. 3, a conductive layer 124 is conformably formed over thesemiconductor structure in both regions A and B shown in FIG. 2,covering the top surface of the dielectric layer 122. In one embodiment,the conductive layer 124 may comprise conductive materials such aspolysilicon, metal or the like, and may have a thickness of about300-2000 Å. The conductive layer 124 may be thicker than the conductivelayer 120.

In FIG. 4, patterned mask layers 126 a and 126 b are respectively formedover a portion of conductive layer 124 (see FIG. 3) in regions A and B,and an etching process 128 is performed to remove the portion of theconductive layer 124 not covered by the patterned mask layer 126 a and126 b. As shown in FIG. 4, the patterned mask layer 126 a and 126 b maycomprise material such as photoresists or the like, and the etchingprocess 128 can be, for example, a dry etching process. The etchingprocess 128 stops on the dielectric layer 122, thereby forming apatterned conductive layer 124 a in region A and a patterned conductivelayer 124 b in region B. The patterned conductive layer 124 a in regionA is formed over a portion of the gate structure in region A and aportion of the semiconductor substrate 100 adjacent to the gatestructure, and the patterned conductive layer 124 b in region B isformed over a portion of the gate structure but is not over thesemiconductor substrate 100.

In FIG. 5, another etching process 129 is performed next to remove theportion of the dielectric layer 122 (see FIG. 4) not covered by thepatterned mask layer 126 a and 126 b, and the patterned conductive layer124 a and 124 b. The etching process 129 can be, for example, a dryetching process. As shown in FIG. 5, the etching process 129 stops onthe conductive layer 120 and the substrate 100, thereby respectivelyforming a patterned dielectric layer 122 a in region A and a patterneddielectric layer 122 b in region B. The patterned dielectric layer 122 ain region A is formed under the patterned conductive layer 122 a andover a portion of the gate structure in region A and a portion of thesemiconductor substrate 100 adjacent to the gate structure, and thepatterned dielectric layer 122 b is formed under the patternedconductive layer 124 b in region B and is formed over a portion of thegate structure but is not over the semiconductor substrate 100.

In FIG. 6, after removal the patterned mask layers 126 a and 126 b shownin FIG. 5, another gate structure G3 comprising the patterned conductivelayer 124 a and the patterned dielectric layer 122 a is formed in regionA, covering a portion of about 20%-80% of a top surface of theunderlying gate structure G1 comprising the conductive layer 120 and thedielectric layer 118. In addition, yet another gate structure G4comprising the patterned conductive layer 124 b and the patterneddielectric layer 122 b is formed in region B, covering a portion ofabout 70%-90% of a top surface of the underlying gate structure G2comprising the conductive layer 120 and the dielectric layer 118.

As shown in FIG. 6, in region A, the gate structure G3 comprising thepatterned conductive layer 124 a and the patterned dielectric layer 122a, and the gate structure G1 comprising the conductive layer 120 and thedielectric layer 118 may be combined to function as a combined gate of asemiconductor device capable of high-voltage operations, and the dopedregion 114 and the doped region 116 may function as source and drainregions, respectively. Through the use of the combined gate shown inFIG. 6, a more uniform electrical field contribution can be observed inthe portion of the well region 110 underlying the combined gate duringoperations of the semiconductor device shown in FIG. 6 when comparedwith another semiconductor device that is similar to the one shown inFIG. 6, but which comprises only the gate structure G1 comprising aconductive layer 120 and a dielectric layer 118 and a dielectric layer122. Accordingly, the semiconductor device capable of high-voltageoperation shown in FIG. 6 can operate at a higher voltage of about 9-100volts, which is about 100-1100% higher than a semiconductor device thatis similar to the one shown in FIG. 6, but which comprises only the gatestructure G1 comprising a conductive layer 120 and a dielectric layer118 and a dielectric layer 122.

Moreover, in region B shown in FIG. 6, the conductive layer 124 b, thedielectric layer 122 b and the conductive layer 120 form an additionalcapacitor which can be simultaneously formed during formation of thesemiconductor device capable of high-voltage operations shown in regionA of FIG. 6.

As shown in FIG. 6, for the ease of illustrating the electricalpotential provided to the combined gate in region A and the capacitor inregion B, conductive contacts 128 a, 128 b, 128 c and 128 d, andconductive lines 130 a, 130 b, and 130 c can be further provided to thesemiconductor structure. In region A, the conductive contact 128 a isconnected to the conductive layer 120 and the conductive contact 128 bis connected to the conductive layer 124 a, and the conductive contacts128 a and 128 b are both connected the conductive line 130 a, so thatthe gate structure G3 comprising the patterned conductive layer 124 aand the patterned dielectric layer 122 a and the gate structure G1comprising the conductive layer 120 and the dielectric layer 118 may beprovided with the same electrical potential during operations. Inaddition, in region B, the conductive layer 124 b is connected to theconductive contact 128 c and the conductive line 130 b, and theconductive layer 120 is connected to the conductive contact 128 d andthe conductive line 130 c. The conductive lines 130 b and 130 c may beprovided with different electrical potentials during operations, so thata capacitor can be formed by the conductive layers 124 b and 120 and thedielectric layer 122. In one embodiment, the conductive contacts 128 a,128 b, 128 c and 128 d may comprise conductive materials such astungsten, copper or the like, and conductive lines 130 a, 130 b, and 130c may comprises materials such as tungsten, copper or the like.

While the invention has been described by way of example and in terms ofthe preferred embodiments, it is to be understood that the invention isnot limited to the disclosed embodiments. On the contrary, it isintended to cover various modifications and similar arrangements (aswould be apparent to those skilled in the art). Therefore, the scope ofthe appended claims should be accorded the broadest interpretation so asto encompass all such modifications and similar arrangements.

What is claimed is:
 1. A semiconductor device, comprising: asemiconductor substrate having a first conductivity type; a first wellregion formed in a portion of the semiconductor substrate, having asecond conductivity type that is the opposite of the first conductivitytype; a second well region formed in a portion of the first well region,having the first conductivity type; a first gate structure formed over aportion of the second well region and a portion of the first wellregion; a first doped region formed in a portion of the second wellregion, having the second conductivity type; and a second doped regionformed in a portion of the first well region, having the secondconductivity type; and a second dielectric layer formed over a portionof the first gate structure, a portion of the first well region, and aportion of the second doped region, wherein the second dielectric layerhas a portion not vertically overlapped with a first dielectric layer ofthe first gate structure.
 2. The semiconductor device as claimed inclaim 1, wherein the first gate structure further comprises a firstconductive layer formed over the first dielectric layer, and the secondgate structure further comprises a second conductive layer formed overthe second dielectric layer.
 3. The semiconductor device as claimed inclaim 2, further comprising: an isolation element disposed in a portionof the semiconductor substrate; a third conductive layer formed over theisolation element; a third dielectric layer formed over the thirdconductive layer; and a fourth conductive layer formed over the thirddielectric layer.
 4. The semiconductor device as claimed in claim 3,wherein the third conductive layer, the third dielectric layer, and thefourth conductive layer form a capacitor.
 5. The semiconductor device asclaimed in claim 3, wherein the third conductive layer and the secondconductive layer are formed simultaneously.
 6. The semiconductor deviceas claimed in claim 3, wherein the third dielectric layer and the seconddielectric layer are formed simultaneously.
 7. The semiconductor deviceas claimed in claim 3, wherein the fourth conductive layer and thesecond conductive layer are formed simultaneously.
 8. The semiconductordevice as claimed in claim 3, wherein the first conductivity type isP-type and the second conductivity type is N-type.
 9. The semiconductordevice as claimed in claim 3, wherein the first dielectric layer has athickness of about 23-140 Å, and the second and third dielectric layershave a thickness of about 200-1200 Å.
 10. The semiconductor device asclaimed in claim 3, wherein the second dielectric layer covers about20%-80% of a top surface of the first gate structure.
 11. Thesemiconductor device as claimed in claim 3, wherein second conductivelayer comprises polysilicon or metal.
 12. A semiconductor device,comprising: a semiconductor substrate having a first conductivity type;a first well region formed in a portion of the semiconductor substrate,having a second conductivity type that is the opposite of the firstconductivity type; a second well region formed in a portion of the firstwell region, having the first conductivity type; a first gate structureformed over a portion of the second well region and a portion of thefirst well region; a first doped region formed in a portion of thesecond well region, having the second conductivity type; and a seconddoped region formed in a portion of the first well region, having thesecond conductivity type; and a second conductive layer formed over aportion of the first gate structure, a portion of the first well region,and a portion of the second well region, wherein the second conductivelayer has a portion not vertically overlapped with a first dielectriclayer of the first gate structure.
 13. The semiconductor device asclaimed in claim 12, wherein the first gate structure further comprisesa first conductive layer formed over the first dielectric layer, and thesecond gate structure further comprises a second dielectric layer formedunder the second conductive layer.
 14. The semiconductor device asclaimed in claim 13, further comprising: an isolation element disposedin a portion of the semiconductor substrate; a third conductive layerformed over the isolation element; a third dielectric layer formed overthe third conductive layer; and a fourth conductive layer formed overthe third dielectric layer.
 15. The semiconductor device as claimed inclaim 14, wherein the third conductive layer, the third dielectriclayer, and the fourth conductive layer form a capacitor.
 16. Thesemiconductor device as claimed in claim 14, wherein the thirdconductive layer and the second conductive layer are formedsimultaneously.
 17. The semiconductor device as claimed in claim 14,wherein the third dielectric layer and the second dielectric layer areformed simultaneously.
 18. The semiconductor device as claimed in claim14, wherein the fourth conductive layer and the second conductive layerare formed simultaneously.
 19. The semiconductor device as claimed inclaim 12, wherein the first conductivity type is P-type and the secondconductivity type is N-type.
 20. The semiconductor device as claimed inclaim 12, wherein second conductive layer comprises polysilicon ormetal.
 21. A semiconductor device, comprising: a semiconductor substratehaving a first conductivity type; a first well region formed in aportion of the semiconductor substrate, having a second conductivitytype that is the opposite of the first conductivity type; a second wellregion formed in a portion of the first well region, having the firstconductivity type; a first gate structure formed over a portion of thesecond well region and a portion of the first well region; a first dopedregion formed in a portion of the second well region, having the secondconductivity type; and a second doped region formed in a portion of thefirst well region, having the second conductivity type; and a secondstructure formed over a portion of the first gate structure, a portionof the first well region, and a portion of the second doped region,wherein the second structure has a portion not vertically overlappedwith a first dielectric layer of the first gate structure.